Detergents used in automated car washes usually include two constituents: inorganic alkaline builders and organic surfactants. These detergents are typically delivered to car wash operators in concentrated liquid and powdered forms. Various problems, however, limit the concentration at which detergents can be distributed and reduce profits.
Because of their instability, liquid detergents must be diluted with water and enhanced with stabilizers to prevent their breakdown during transit and storage. The disadvantages associated with increasing the amount of water in a detergent are many, with manufacturing, packaging, transporting, and handling costs rising in proportion to the amount of water added. Of course, highly concentrated liquid surfactants, absent the usual inorganic compounds, can be bought, but they are considered to be less effective cleaners.
Detergents, delivered in powdered form, typically include a mix of finely divided phosphates, silicates and carbonates as well as a small amount of evenly distributed liquid surfactant. Generally, the surfactant concentration in the resulting detergent composition is limited to approximately 15 percent by weight. Excess amounts of the surfactant result in lumpy powders that will not flow through state of the art blending and dispensing equipment.
Dispensing a powdered detergent in a modern car wash is difficult. Hand measurement of the detergent by inexperienced workmen is time consuming and prone to mistake. Spraying an overly concentrated detergent onto a car is, of course, wasteful and can be harmful to the finish of the car. Further, prolonged and unchecked dampness can lead to consolidation of the powdered material into a solid block.
In an effort to overcome some of these problems, Barton Lockhart of Corsicana, Tex., proposed an improved detergent mixing system in U.S. Pat. Nos. 5,439,020 and 5,678,593. Lockhart uses a tank for dissolving powdered, inorganic, detergent constituents in water until a saturated detergent base is formed. With a venturi, the saturated detergent base is drawn from the tank and mixed with a surfactant and other liquid detergent constituents to make a complete detergent liquid.
The use of Lockhart's system by car wash operators throughout the United States for nearly a decade has shown it to be practical and cost-effective, but problems have occasionally arisen for some operators. For example, undissolved inorganics sometimes flow from the mixing tank in the detergent base, blocking downstream flow. It has been found, however, that injecting a small amount of water into the flow line conveying the saturated detergent base from the mixing tank causes any undissolved material to dissolve and inhibits the growth of crystals comprising dissolved inorganic material. Unfortunately, this injection of water makes it difficult to determine the exact concentration of saturated detergent base in the final detergent mix. Furthermore, water injection adds to the complexity of the system and can be a source of mistakes and confusion by operators of the system.